Obtaining irish citizenship through grandfather

Hi - my grandfather,who had a very common Irish surname, which I retain, was born before 1917 in Ireland - when the Dublin Records Office was destroyed. I am interested in obtaining an Irish Passport - currently mostly living in UK but also spend time in France. I cannot find his birth certificate. Would it be possible to get the Passport without it? My parents divorced when I was very young and I have no knowledge of him except from English censors records stating he was born in Ireland ( but not where) and his marriage certificate in England. My mother always said my father was ''Irish'' but he was born in England. Many thanks.